Personal computer printers and the like employ ink jet recording technology. Ink jet recording apparatus have several advantages, such as easy handling, superior print performance, and low cost. Because of these benefits, ink jet recording apparatus have now become widespread. There exist various types of ink jet recording apparatus and they are classified according to how ink droplet is emitted. For example, there is an ink jet recording apparatus of the thermal type in which thermal energy is utilized to create a bubble in ink, and a droplet of the ink is emitted by a pressure wave caused by the created bubble. There is another ink jet recording apparatus of the electrostatic type in which an ink droplet is sucked and emitted by electrostatic force. There is still another ink jet recording apparatus of the piezoelectric type in which an ink droplet is ejected by means of an oscillator such as a piezoelectric element. In addition to these ink jet recording types, Japanese Unexamined Patent Gazette No. H05-278212 further discloses an ink jet recording apparatus which is a combination of the piezoelectric type and the electrostatic type.
Whichever of the foregoing ink jet recording types is employed, ink droplets are emitted from many nozzles formed in an ink jet head in an ink jet recording apparatus. These emitted ink droplets land on a sheet of recording paper to form an ink dot. Then, by properly arranging many dots, printing of characters or images is performed on the recording paper sheet.
However, in a typical ink jet recording apparatus, the number of ink droplets each nozzle emits during one print cycle is limited to one. This means that dot density (i.e., the number of dots per unit area) depends upon nozzle density (i.e., the number of nozzles formed in an ink jet head per unit area). Therefore, in order to provide an improved dot density, the nozzle density must be improved.
However, with conventional ink jet head structures, it is difficult to provide improved nozzle densities for cost reasons. Accordingly, it has been considered that rapid improvement in dot density is difficult to achieve.
Further, another problem arises. That is to say, the landing positions of ink droplets emitted through each nozzle align in line in a scanning direction. This results in the occurrence of a so-called white stripe due to the deviation of landing positions in a direction normal to the scanning direction, and due to the variation in ink-droplet emission volume among nozzles. Such white striping causes the quality of printing of characters and images to deteriorate.
Bearing in mind the above-described problems with the prior art techniques, the present invention was made. Accordingly, an object of the invention is to provide improvement in the quality of printing of characters or images by heightening the dot density or by reducing the occurrence of white striping.